Variable inductance device

ABSTRACT

A variable inductance device which has a magnetic core having two coils thereon, the two coils being not coupled magnetically to each other. The inductance of one of the two coils is controlled by a DC current flowing through the other of said two coils. The device has a high Q-value, and a wide range of inductance is produced by a small DC current. The device is useful in tuned circuits of various electronic instruments.

United States Patent [72] Inventors Eiichi Hirota;

Yutaka Neichi; Minoru Sugirnura, all of Osaka-tu, Japan [21] Appl. No.855,574

[22] Filed Sept. 5, 1969 [45] Patented Dec. 28, 1971 [73] AssigneeMatsushita Electric Industrial Co., Ltd.

Osaka, Japan [54] VARIABLE INDUCTANCE DEVICE 6 Claims, 9 Drawing Figs.

[52] U.S. Cl 336/155, 336/184, 336/212, 336/233 [51] Int. Cl 1-101121/08[50] Field oiSearch 336/212,

[56] References Cited UNITED STATES PATENTS 3,415,751 12/1968 Hirota eta1 252/6259 1,601,400 9/1926 Latour 1,628,398 5/1927 Casper et al336/212 X 2,064,773 12/1936 Vogt.... 336/212 X 2,846,637 8/1958 Huge336/155 X 2,996,695 8/1961 Dickinson 336/212 X 3,189,859 6/1965 Olsen336/212 3,188,552 6/1965 Owen 323/48 2,932,787 4/1960 Krabbe et al.336/155 X 2,911,586 11/1959 Zeling 336/155 OTHER REFERENCES Bozorth,Ferromagnetism, D. Van Norstrand Company, Inc., l96l,pp. 870- 871.

Primary Examiner-Thomas J. Kozma Attorney-Wenderoth, Lind & PonackABSTRACT: A variable inductance device which has a magnetic core havingtwo coils thereon, the two coils being not coupled magnetically to eachother. The inductance of one of the two coils is controlled by a DCcurrent flowing through the other of said two coils. The device has ahigh Qvalue, and a wide range of inductance is produced by a small DCcurrent. The device is useful in tuned circuits of various electronicinstruments.

PATENTED niczamn 3353153 4 saw 1 or 2 INVENTORS EIICHI HIROTA -YUTAKANEICHI MINORU SIGIMURA ATTORNEYS 1 VARIABLE INDUCTANCE DEVICE Thisinvention relates to a variable inductance device, the inductance ofwhich is controlled by means of a DC current. Such a device can be usedin the tuned circuits of radio receivers and other electronicinstruments, especially for tuned circuits of automatically controlledelectronic instruments.

Prior art variable inductance devices controllable by DC currents haveconsisted of a toroidal-shaped magnetic core with two coils wound on thecore. The magnetic inductance L of one of these two coils is controlledby a DC current flowing through the other of the coils. This prior artdevice has a low Q-value because the high-frequency coil is directlycoupled to the DC current coil, and the DC current coil has a very lowimpedance. To correct this problem, prior art devices have a chockingcoil having large inductance connected in series to the DC current coilto increase the impedance of the DC current coil. This arrangement isusually large and complex and, moreover, requires a large DC current toobtain the desired range of variable inductance.

A variable inductance device for high frequency use usually includes amagnetic core of ferrite material. The high-electrical resistivity offerrite materials assures a high Q-value of the inductance device. Butthe ferrite core is also required to have a widely variable range ofpermeability, since a large DC current is necessary for obtaining thedesired range of variable inductance. This means that the ferritematerial used in the variable inductance device must have a high-initialpermeability and a low-magnetic loss in high-frequency ranges. Thedevices must also be stable under varying environmental conditions.Therefore, ferrite materials used in the devices must have lowmagnetichysteresis, small temperature coefficients of permeability and lowdecrease in permeability with time, i.e., low disaccomodation (D.A.).The disaccomodation, D.A., means a time decrease of permeability asdefined in e14 of Snoeks New Development in Ferromagnetic OxideMaterials, Elsvier Publishing Co., New York, I949.

An object of the present invention is to provide a variable inductancedevice which requires only a low amount of DC current to obtain thedesired variable range of inductance.

A further object of the present invention is to provide a variableinductance device having a high Q-value and a high stability underchanging environmental conditions.

A still further object of the invention is to provide a variableinductance device comprising an improved magnetic core which consists ofa novel ferrite composition suitable for the present purpose.

These objects are achieved by a novel variable inductance deviceaccording to the present invention which comprises a magnetic corehaving two coils thereon, said two coils not being coupled magneticallyto each other, whereby the inductance of one of said two coils iscontrolled by a DC current flowing through the other of said two coils.

These and other objects will be apparent upon consideration of thefollowing description taken together with the accompanying drawings,wherein:

FIG. I is a schematic diagram of a variable inductance device accordingto the present invention;

FIG. 2a is a perspective view of E-shaped and I-shaped magnetic bodieswhich are combined to form a magnetic core of one embodiment of thepresent invention;

FIG. 2b is a schematic diagram of a variable inductance device made ofthe magnetic bodies of FIG.

FIG. 3a is a perspective view of an Ishaped magnetic body and a magneticbody having a cutout therein, the said two bodies being combined to forma magnetic core of a second embodiment of the present invention;

FIG. 3b is a schematic diagram of a variable inductance device made ofthe magnetic bodies of FIG. 312;

FIG. 4a and 4b are magnetic cores having two windows and consisting oftwo magnetic bodies combined through the insertion of magnetic materialhaving a magnetic permeability higher than that of said magnetic bodiesin accordance with the present invention; and

FIGS. 5 and 6 are curves of tuned frequency versus DC current and of Qversus DC current relations which are exhibited by the present inventionwhen used in tuned circuits.

Before proceeding with a detailed description of a variable inductancedevice according to the present invention, the principal construction ofthe inductor device will be explained with reference to FIG. 1 of thedrawings wherein reference character 11 designates a magnetic corehaving two windows 14 and 14' formed therein. A coil 12 is wound on aportion 16 between said two windows 14 and 14'. Another coil 13 is woundon two portions 15 and 15 formed between the core periphery and saidwindow 14 and between the core periphery and said window 14'. It isimportant that the two coils l2 and 13 are not magnetically coupled toeach other. The inductance of one of said two coils 12 and 13 iscontrolled by a DC electric current flowing through the other of saidtwo coils l2 and 13. When DC current flows through the coil 12. magneticfluxes d) and are induced in core portions 15 and 15', respectively. Thecoil winding 13 on the portion 15 is wound clockwise to the flux qb andon the portion 15 is wound counterclockwise to the flux d), and hasnumbers of turns N and N at core portions 15 and 15, respectively. Thecoil windings l2 and 13 do not couple magnetically with each other whenN=N'. Under this condition, when a high-frequency voltage is applied tocoil 13, no voltage is induced in coil 12. The coil 13 has a largeQ-value, regardless of the small impedance of the coil 12. Therefore,the variable inductance device according to the present invention doesnot need the choke coil used in prior art devices.

It has been discovered according to the present invention that themagnetic core 11 having two windows is easily constructed in thefollowing way. Referring to FIGS. 2a and 2b, the magnetic core 11 havingtwo windows 14 and 14' consists of an E-shaped magnetic body 17 and anI-shaped magnetic body 18 which are combined together to form said corehaving two windows 14 and 14. Another arrangement is shown in FIGS. 3aand 3b, in which the magnetic core 11 consists essentially of a magneticbody 19 having a cutout 22 therein and an I-shaped magnetic body 20, thetwo bodies being combined to form said core having two windows 14 and14'.

When the magnetic core 11 is formed by combining magnetic bodies 17 and18 or 19 and 20, the core must have no airgap at the surfaces at whichmagnetic bodies 17 and 18 or 19 and 20 come into contact with eachother. An airgap at these surfaces would decrease the variable range ofinductance or would necessitate the use of a larger DC current forobtaining the desired variable range of inductance. It is desirable tocombine the two magnetic bodies 17 and 18 or 19 and 20 by means of aninsertion 21 of magnetic material having magnetic permeability higherthan that of said magnetic bodies as shown in FIGS. 4a and 4b.

The present inductance device can be used in the tuned circuit of aradio receiver. In this application the variable range of inductancemust cover the range of radio-signals in a broadcast band, i.e., a rangebetween about 500 to 1,650 kHz. The tuned frequency f is inverselyproportional to the square root of inductance of the device, i.e. f QC1/ V An inductance of an inductance device is linearly proportional tothe magnetic core 11. The permeability of magnetic core 11 decreaseswith an increase in the DC current ln order to cover the frequencyrang-e of SOUTO ITGSURHZItBe 'Lfieifthe permeability of the coil 11 mustsatisfy the following relations:

vp ht fl ,650 (kHz.)/500(kHz.), eon/#1350 wherein #501 and m areperrneabilities at DC currents which make the tuned frequencies of tunedcircuit 500 kHz. and 1,650 kHz., respectively. The DC current necessaryfor the u will be defined as the maximum DC current. In other words, themaximum DC current defined herein is a DC current which is necessary forachievement of the lowest inductance in the desired variable inductancerange. It has been discovered according to the present invention thatthe maximum DC current is lowered by using a variable inductance deviceaccording to the present invention in association with the ferritematerial specified below.

The specified ferrite material is Mn-Zn-ferrite, which consistsessentially of 52 to 55 mol percent of Fe O 8 to 18 mol percent of ZnOand the balance being MnO and an additive combination of 0.05 to 1percent by weight of GeO and 0.05 to 1 percent by weight of CaO. Avariable inductance device comprising this specific ferrite material notonly provides a wider range of variable inductance, but also exhibitsimproved properties such as low loss in a high frequency use,low-magnetic hysteresis and small temperature coefficient ofpermeability and low disaccomodation.

The following examples are meant to be illustrative preferredembodiments of the invention, but are not meant to limit the scopethereof.

EXAMPLE 1 A mixture of 54 mol% E6 30 mol% MnO, 16 mol% ZnO and 0.1 wt.6e0 0.4 wt.% CaO is calcined at 800 C. for 2 hours in air. The calcinedpowder is then molded into E- shaped and I-shaped bodies. The pressedbodies are heated to l 1 80 C. in air and maintained at that temperaturefor 2 hours in a N -gas atmosphere and cooled to room temperature in Ngas. The obtained ferrite material has magnetic properties as listed intable I. The dimensions of the E-shaped and I-shaped bodies (FIG. 22)are listed in table II.

. TABLE I Permeability 900 Q (at 1 mHz) 50 D.A.= 100,- percentTemperature coefiicient of permeability 15 mo and mm are permeabilitiesat 10 sec. and 1,000 sec. after demagnetieatlon. respectively.

Da-nm. D5095 mm. D==l.80 mrn. D,=2.2 mm.

l D,=3.80 mm. D,=l.00 mm.

D =1.30 mm.

? Sintered E-shaped and I-shaped bodies are combined together to form amagnetic core on which two coils are wound as shown in FIG. 2b. Thenumber of turns of coil 12 at portion 16 is 140 turns and the number ofturns of coil 13 is 77 turns at each portion 15 and 15' of FIG. 2b. TheDC current flows through the coil 12 and controls the inductance of coilI 13. The inductance of coil 13 at a DC current of 10 ma. is 1.2 mh. anddecreases to 0.1 mh. at DC current of 100 ma. Characteristics of thisvariable inductance device are shown in table III. A tuned circuit isformed by using this variable inductance device combined with acondenser of 85 pf. The curve of tuned frequencies versus controlled DCcurrent is given in FIG. 5. The Q-value of this circuit is also shown in55 there]? and an two w ndows.

FIG. 5.

TABLE III wider than (l:l0) smaller than l00 ma. larger than 50 smallerthan kHz.

smaller than IXIO" less than 1% the value necessary for covering thebroadcast band.

weight of C210.

EXAMPLE II The magnetic bodies shown in FIG. 3a are made of a ferriteexactly the same as that of example I. The sintered bodies are combinedto form a magnetic core as shown in FIG. 3b. The dimensions of thesintered bodies are listed in table IV.

TABLE IV D 'nm. D,=0.85 mm. D:=I.55 mm. D5200 mm. D -,=5.3 mrn. D =l.00mm. D =l.55 mrn.

The number of turns of coil 12 at core portion 16 is 120 turns and thenumber of turns of coil 13 is 32 turns at each of the two portions 15and 15 of FIG. 3b. The DC current flows through the coil 12 and controlsthe inductance of coil 13. The inductance of coil 13 at a DC current of10 ma. is 515 ph. and decreases to 75 ,uh. at DC current of ma. A tunedcircuit is formed by using this inductance device combined with acondenser of 205 pf. The curve of tuned frequencies versus controlled DCcurrent is given in FIG. 6. The O-curve of the circuitisals o sl1own irFIG. 6.

We claim:

1. A variable inductance device comprising a magnetic core having twocoils thereon, said two coil windings being not coupled magnetically toeach other, and a source of DC current connected to one of said coils,whereby a wide range of inductance in one of said two coils iscontrolled by a small range of said DC current flowing through the otherof said two coils, said magnetic core comprising a Mn-Zn ferrite whichconsists of 52 to 55 mol percent of Fe O 8 to 18 mol percent of ZnO andthe balance being MnO and as an additive combination, 0.05 to 1 percentby weight of GeO and 0.05 to 1 percent by 2. A variable inductancewherein said magnetic core has two windows formed therein, and one ofsaid two coils is wound on a portion between said two windows and theother of said two coils is wound on two portions formed between a coreperiphery and one of said two windows and between a core periphery andanother of said two windows.

3. A variable inductance device according to claim 2 wherein said corecomprises an E-shaped magnetic body and an I-shaped magnetic bodycombined to form said two windows.

4. A variable inductance device according to claim 2 wherein said corecomprises a magnetic body having a cutout shaped magnetic body combinedto form said 5. A variable inductance device according to claim 3further comprising a magnetic material having magnetic permeabilityhigher than that of said magnetic bodies inserted between said magneticbodies 6. A variable inductance device according to claim 4 furthercomprising a magnetic material having magnetic permeability higher thanthat of said magnetic bodies inserted between said magnetic bodies.

device according to claim 1,

1. A variable inductance device comprising a magnetic core having twocoils thereon, said two coil windings being not coupled magnetically toeach other, and a source of DC current connected to one of said coils,whereby a wide range of inductance in one of said two coils iscontrolled by a small range of said DC current flowing through the otherof said two coils, said magnetic core comprising a Mn-Zn ferrite whichconsists of 52 to 55 mol percent of Fe2O3, 8 to 18 mol percent of ZnOand the balance being MnO and as an additive combination, 0.05 to 1percent by weight of GeO2 and 0.05 to 1 percent by weight of CaO.
 2. Avariable inductance device according to claim 1, wherein said magneticcore has two windows formed therein, and one of said two coils is woundon a portion between said two windows and the other of said two coils iswound on two portions formed between a core periphery and one of saidtwo windows and between a core periphery and another of said twowindows.
 3. A variable inductance device according to claim 2 whereinsaid core comprises an E-shaped magnetic body and an I-shaped magneticbody combined to form said two windows.
 4. A variable inductance deviceaccording to claim 2 wHerein said core comprises a magnetic body havinga cutout therein and an I-shaped magnetic body combined to form said twowindows.
 5. A variable inductance device according to claim 3 furthercomprising a magnetic material having magnetic permeability higher thanthat of said magnetic bodies inserted between said magnetic bodies.
 6. Avariable inductance device according to claim 4 further comprising amagnetic material having magnetic permeability higher than that of saidmagnetic bodies inserted between said magnetic bodies.